The right triangle with angles 30°30°, 60°60°, 90°90° is half of an equilateral triangle: this is where its characteristic ratios between the sides come from.

Theorem — 30°-60°-90° triangle

In a right triangle in which one leg is half the hypotenuse, the acute angles measure 30°30° and 60°60°, and the other leg measures the first leg times 3\sqrt{3}: se c=ip2    c=c3,α=30°,β=60°.\text{se } c = \frac{\text{ip}}{2} \quad\implies\quad c' = c\sqrt{3}, \quad \alpha = 30°, \quad \beta = 60°.

The leg cc is half the hypotenuse 2c2c; the other leg equals c3c\sqrt{3}.

Topics: Euclidean circle
Concepts: Right triangle
Skills: Using formulae